• Linus Torvalds's avatar
    Merge branch 'simplify-do_wp_page' · b25d1dc9
    Linus Torvalds authored
    Merge emailed patches from Peter Xu:
     "This is a small series that I picked up from Linus's suggestion to
      simplify cow handling (and also make it more strict) by checking
      against page refcounts rather than mapcounts.
    
      This makes uffd-wp work again (verified by running upmapsort)"
    
    Note: this is horrendously bad timing, and making this kind of
    fundamental vm change after -rc3 is not at all how things should work.
    The saving grace is that it really is a a nice simplification:
    
     8 files changed, 29 insertions(+), 120 deletions(-)
    
    The reason for the bad timing is that it turns out that commit
    17839856 ("gup: document and work around 'COW can break either way'
    issue" broke not just UFFD functionality (as Peter noticed), but Mikulas
    Patocka also reports that it caused issues for strace when running in a
    DAX environment with ext4 on a persistent memory setup.
    
    And we can't just revert that commit without re-introducing the original
    issue that is a potential security hole, so making COW stricter (and in
    the process much simpler) is a step to then undoing the forced COW that
    broke other uses.
    
    Link: https://lore.kernel.org/lkml/alpine.LRH.2.02.2009031328040.6929@file01.intranet.prod.int.rdu2.redhat.com/
    
    * emailed patches from Peter Xu <peterx@redhat.com>:
      mm: Add PGREUSE counter
      mm/gup: Remove enfornced COW mechanism
      mm/ksm: Remove reuse_ksm_page()
      mm: do_wp_page() simplification
    b25d1dc9
i915_gem_userptr.c 21.7 KB